1. Field of the Invention
The present invention relates to an optical element which has anisotropy in the scattering of linearly polarized light and is highly effective in diffusing the directions of the scattering thereof, and which is suitable for use in, e.g., improving the perceptibility of liquid-crystal displays and the like.
The present application is based on Japanese Patent Application No. Hei. 10-376393 which is incorporated herein by reference.
2. Description of the Related Art
An optical element has conventionally been known which comprises a polarizing plate and superposed thereon a light diffusing plate which is either a plastic film containing fine transparent particles dispersed therein or a plastic film having a roughened surface. This light diffusing plate effectively functions, in transmission type liquid-crystal displays and the like, to diminish the image of the backlight to thereby improve the perceptibility of the devices. However, in reflection type liquid-crystal displays and the like, the conventional optical element has had a problem that the light incident through the light diffusing plate interferes with the outgoing diffused light to cause considerable image fogging or blurring.
The above image fogging or blurring can be reduced by disposing the light diffusing plate so as to be in contact with the liquid-crystal cell. In this constitution, however, the linearly polarized light which has passed through the polarizing plate strikes on the light diffusing plate. As a result, the polarized state is eliminated, leading to a reduced contrast. In particular, in displaying black images, the poorly polarized state leads to white blurring, which is the phenomenon in which a dark image becomes whitish due to scattered light.
On the other hand, other known light diffusing plates include: a diffusing plate which comprises a matrix and, dispersedly contained therein, regions having anisotropy in refractive index and which is anisotropic with respect to the scattering of linearly polarized light; and diffusing plates of the above kind which comprise a combination of a thermoplastic resin and a low-molecular liquid crystal, a combination of a low-molecular liquid crystal and a photocrosslinkable low-molecular liquid crystal, and a combination of poly(vinyl alcohol) and a low-molecular liquid crystal, respectively (see U.S. Pat. No. 2,123,901, WO 87/01822, EP 0506176, and JP-A-9-274108 or the like). (The term “JP-A” as used herein means an “unexamined published Japanese patent application”.) However, these light diffusing plates are unsuitable for practical use, for example, because they are difficult to produce and because when applied to liquid-crystal displays or the like, the diffusing plates have poor handleability and poor stability of functions.